Jewelry rope chain has been known for many decades, both in a hand-made and machine made forms, with machine made forms of these chains generally being limited to less expensive chains, where less precision in the joining of the links of chains is required. However, regardless of the method used to assemble the individual links into the rope chain, the cost of precious metals and their alloys, such as 14 Karat gold and the like used to make the chain is a large component of the final cost of the finished rope chain.
While assembly costs can be decreased by manufacturing rope chain in countries with low labor costs and by introducing labor saving tools and machines, the jewelry manufacturer can do little about the cost of gold, platinum, and other precious metal, which are almost identical around the world. Therefore, there is a strong need for the manufacture of rope chain designs which, while preserving the same look (and also width of chain) as conventional chain designs, in fact, use substantially less precious metal per unit length.
In order to gain a better understanding of the solution to the objective of saving precious metals in making rope chain, it is instructive to review the basics of rope chain manufacture. All rope chains are assembled from a large number of annular link members with gaps. Such a typical link 10 is shown in FIGS. 1-3. Traditionally, these links have been either solid 10 (FIGS. 2a or 2b) or hollow 10a (FIG. 3) and either having a generally rectangular or circular cross-sections FIG. 2a or FIG. 2b. By arranging series of these rings with their gaps G alternately facing up and down, e.g. as described in Benhamou, et al. U.S. Pat. No. 4,651,517 the rope chain is gradually built up, held in place with a forming wire 12, and soldered at points S to form the rope chain shown in FIG. 4.
In these prior art chains, the individual links 10 are chosen so that the central opening Di in the ring 10 has a diameter slightly greater than three times greater than the widest portion of the link wire Dw, for example, 3.4 times greater. Arranged in this way, four links would make up the basic, repeating, series of links used to form the chain.
U.S. Pat. No. 4,651,517 to Benhamou, et al. discusses the prior art rope chains in great detail, and discloses an improvement over the traditional prior art method in saving precious metal for an equivalent length and width of finished rope chain whereby instead of using a series of four repeating rings arranged as shown in FIGS. 5a-5d therein, a series of 6, 8 or more even number of links, each having a larger internal diameter compared to the ring cross-sections of the prior art chains are used to save material as shown in FIGS. 8a-8g therein. Additionally U.S. Pat. No. 4,996,835 to Rozenwasser and S.I.L.O. patent DM014648 illustrate rope chains wherein the links are non-circular in shape, in order to save precious metal.
These prior art rope chains utilize links in which the wire cross-sections thereof are basically circular, or rectangular with rounded corners. Although the shapes of the prior art links achieve the goal of allowing the manufacturer to save precious metal, for a given width and length of chain, their use generally results in increased labor costs since a greater number of links must be assembled to make a rope chain having the same length and width. Moreover, as the number of links per unit length increases, the chains may become more difficult to assemble.
It has also been known in the prior art of making flat chains to use precious metal wire having a triangular cross-section, with one corner of the triangle defining the outermost perimeter of each link member. The applicant himself has previously made rope chains with wire having a triangular cross-section, with one corner of the triangle defining the outermost perimeter of the wire once formed into the individual link members. Although material is saved, rope chains assembled from such wire have a somewhat corrugated appearance and feel sharp to the touch. Thus rope chains made from triangular link wire formed into link members with one corner of the wire defining the outer perimeter of the link members are not as desirable as prior art chains made of "smoother" link wire from the standpoint of appearance and feel of the finished rope chain. There is accordingly a need for rope chain which is formed in a way to save material, but which can be assembled without using a greater number of links per unit length, and which also results in a smooth, tight, and non-corrugated appearance.